I have a stack of sociology and demographics books I have just barely started in on, but one notable feature is that they use “upper middle” and “lower middle” to split the middle class into two halves. It’s a deliberate use of terminology to eliminate the conceptual notion of a broad middle class when doing social analysis.
The upshot is, of course, that college and university credentials are pretty much always “upper” regardless of pay level, while exam-based credentials and trade licenses are always lower. It’s the darnedest thing. The dental hygienist by the sociological split is lower-middle because it’s usually a certificate program, but the claims processor for the dental office is upper-middle because you need a college degree for her job. Both pay pretty similarly, but that isn’t the point. Public school teachers are upper middle as well by this professional sociological view, but daycare employees are lower middle.
And yes, the average IT worker is lower middle because not only can you still get a job without a four year degree, there is a system of hiring “outside the box” evolving to codify the process. But the project manager making half to a third of the money is upper middle because there is no way to get that job without a degree.
Class anxiety is a thing, and one way to mask it is to carefully define big chunks of STEM as lower middle in a formal taxonomy, or simply only talk of “upper middle” in terms of doctors, lawyers and other pre-internet professions. The blue/white collar melding that the T and E in STEM tend to represent doesn’t lend itself perfectly to the university-based degree march, so it’s easier for (usually) lower-earning class-anxious college graduates with three degrees to pretend they don’t exist and that the ones who do are just lower middle and overpaid anyway.
It’s also easier to codify the whole process to make it look scientific and “evidence-based”.
So the people who study middle classness don’t, for the most part follow the popular three-tier split into upper middle, middle middle and lower middle. It’s A or B for them.